Three-phase voltage tripling rectifier circuit

ABSTRACT

A circuit for rectifying and tripling an input voltage from a three-phase source is described. The three-phase input voltage source is connected to the circuit via a wye connected secondary transformer, winding. The center point of the wye connected winding is connected to the midpoint of first and second series connected output capacitors. The other sides of the first and second output capacitors are connected to first and second output terminals respectively. The end of each leg of the three wye connected windings are connected through the second output terminal through a separate reverse biased diode. The end of each leg of the three wye connected windings are also connected through a separate capacitor to the mid-point of separate pairs of two diodes connected in series. One of the diodes of each pair is connected in reverse bias to the mid-point of the output capacitors and the other diode of each pair is connected in forward bias to the first output terminal. Thus, each of the three wye connected windings are connected through circuits including diodes and capacitors and the circuits are connected in parallel across the output terminals to provide a rectified output voltage which is three times the magnitude of the input voltage.

United States Patent 1191 Zarowin Oct. 9, 1973 THREE-PHASE VOLTAGETRIPLING RECTIFIER CIRCUIT OTHER PUBLICATIONS Analysis of theVoltage-Tripling and Quadrupling Rectifier Circuits, D. L. Waidelich &1-1. A. K. Taskin, l.R.E. Vol. 33, No. 7, July, 1945, pp. 449-453. KepcoPower Supply Handbook, Kepco, lnc., Flushing, N.Y., page 8, 1966.

Primary Examiner-William M. Shoop, Jr. Attorney-John .1. Goodwin et a1.

[ 5 7 ABSTRACT A circuit for rectifying and tripling an input voltagefrom a three-phase source is described. The threephase input voltagesource is connected to the circuit via a wye connected secondarytransformer, winding. The center point of the wye connected winding isconnected to the midpoint of first and second series connected outputcapacitors. The other sides of the first and second output capacitorsare connected to first and second output terminals respectively. The endof each leg of the three wye connected windings are connected throughthe second output terminal through a separate reverse-biased diode. Theend of each leg of the three wye connected windings are also connectedthrough a separate capacitor to the mid-point of separate pairs of twodiodes connected in series. One of the diodes of each pair is connectedin reverse bias to the mid-point of the output capacitors and the otherdiode of each pair is connected in forward bias to the first outputterminal. Thus, each of the three wye connected windings are connectedthrough circuits including diodes and capacitors and the circuits areconnected in parallel across the output terminals to provide a rectifiedoutput voltage which is three times the magnitude of the input voltage.

3 Claims, 2 Drawing Figures ss i 3V sa i r r PATENIEUUBT 919M 3.764.886

FIG. 1 1k PRIOR ART INVENTOR CHARLES B. ZAROWIN BY 50% 8. 3M

ATTORNEY THREE-PHASE VOLTAGE TRIPLING RECTIFIER CIRCUIT BACKGROUND OFTHE INVENTION 1. Field of the Invention The present invention lies inthe field of voltage tripling rectifier circuits.

2. Prior Art US. Pat. No. 3,525,031 to WL. King, issued Aug. 18, 1970and assigned to Nathan E. Knecht describes a voltage multiplier andrectifier circuit which is connected to a three-phase A.C. source. Thepresent invention is distinct from this prior art in that the prior artcircuit is not symmetrical and merely raises the level of the inputvoltage wave, does not reduce ripple voltage and therefore does notprovide a significant improvement over single phase operation.

SUMMARY OF THE INVENTION An object of the present invention is toprovide a voltage tripling rectifier circuit for use with a threephaseinput voltage signal.

Another object of the present invention is to provide a three-phasevoltage tripling rectifier circuit having symmetrical circuits connectedin parallel.

A further object of the present invention is to provide a three-phasetripling rectifier circuit having to provide an output signal having aripple voltage significantly less than that for single phase operation.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of a preferred embodiment of the invention, as illustratedin the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic circuit diagramof a prior art single phase voltage tripling rectifier circuit.

FIG. 2 is a schematic circuit diagram ofa three-phase voltage triplingrectifier circuit according to the principles of the present invention.

Referring to FIG. 1, a circuit is shown which represents a prior artsingle phase voltage tripling rectifier circuit. The circuit includes asingle phase A.C. source. One side of A.C. source is connected to themidpoint of two series connected output capacitors 12 and 14 acrosswhich output terminals 16 and 18 are connected. The other side of A.C.source 10 is connected through back-biased diode 20 to output terminal18. The other side of A.C. source 10 is also connected through acapacitor 22, the mid-point of two diodes 24 and 26 connected in series.The back side of diode 26 is connected to the mid-point of capacitors l2and 14 and the forward side of diode 24 is connected to output terminal16.

In operation, the positive half cycle of voltage is produced from source10 and cannot pass through diode 20. The positive half cycle of voltagecharges capacitor 22 and a negative voltage appears at the junction ofdiodes 24 and 26. The negative voltage at the junction of diodes 24 and26 causes a current flow through diode 26 to the junction of capacitorsl2 and 14. The voltage V is distributed at the capacitors l2 and 14 inaccordance with their respective values. For example, if the value ofcapacitor 12 is equal to the value of capacitor 14, both capacitors arecharged to V/2. When capacitors l2 and 14 are charged, the outputvoltage across terminals 16 and 18 is equal to V.

When the negative half cycle of input voltage occurs, current flowsthrough diode 20 to charge capacitor 14. Capacitor 22 also gets chargedin the opposite direction and capacitor 22 stays charged due to diode24. Thus, capacitors l2 and 14 contain a total charge of 2V and thepotential across output terminals 16 and 18 is 2V.

Upon the occurrence of the next positive half cycle of input voltagecapacitor 12, charges to a value of 2V and the charge on capacitor 14remains the same (V) so that the voltage across the output terminals 16and 18 is 3V. For all further cycles, the output voltage across outputterminals 16 and 18 is 3V. Thus, after an initial build up period ofthree cycles, the output across terminals 16 and 18 is a rectifiedvoltage three times the value of the input voltage.

An important factor in the performance of a rectifier circuit is theamount of ripple present in the output voltage. Ripple is undesirableand should be minimized or eliminated if possible. Ripple is an inversefunction of the product of frequency, resistance and capacitance (wRC)of the rectifier circuit. If the circuit operates at a frequency of 60Hertz, the load resistance R decreases in order to increase the poweroutput. Thus, the capacitance C must be increased in order to limit theripple amplitude. Since there are practical constraints on the physicalsize of the capacitors that can be used, reduction of the amount ofripple in the single phase prior art circuit shown in FIG. 1, can onlybe accomplished by increasing frequency and/or load resistance.

Referring to FIG. 2, a unique voltage tripling rectifier circuitoperating from a three-phase input voltage is illustrated. Thethree-phase voltage source in the embodiment is a wye connectedthree-phase transformer secondary winding 30 having three legs 30A, 30Band 30C. The center of secondary winding 30 is connected to the junctionof two output capacitors 32 and 34 which are connected across outputterminals 36 and 38. The ends of each of the legs 30A, 30B and 30C arerespectively connected to three identical circuits each composed ofthree diodes and a capacitor.

The end of leg 30A is connected through a back biased diode 40 to outputterminal 38 and through capacitor 42 to the junction of a pair of diodes44 and 46. The back of diode 46 is connected to the junction of outputcapacitors 32 and 34 and the front of diode 44 is connected to outputterminal 36. Likewise, the end of leg 30B is connected through backbiased diode 48 to output terminal 38 and through capacitor 50 to thejunction of diodes 52 and 54. The back of diode 54 is connected to thejunction of output capacitors 32 and 34 and the front of diode 52 isconnected to output terminal 36. In the same manner, the end of leg 30Cis connected through back biased diode 56 to output terminal 30 andthrough capacitor 58 to the junction of diodes 60 and 62. The back ofdiode 62 is connected to the junction of output capacitors 32 and 34 andthe front of diode 60 is connected to output terminal 36.

From the aforesaid description, it is seen that each of the legs ofwinding 30 are symmetrically connected through a rectifier circuitcomposed of three diodes and a capacitor. The three rectifier circuitsare connected in parallel across output terminals 36 and 38. If each ofthe capacitors 42, 50 and 58 have a value of C,

then capacitors 32 and 34 have values three times as large (3C).

A three-phase AC signal is produced at winding 30. A sinusoidal ACsignal appears across each leg 30A, 30B and 30C with a phase differenceof 120 degrees. The positive half cycle of the signal on leg 30A isblocked but diode 40 charges capacitor 42. A negative voltage thereforeappears at the junction of diodes 44 and 46 causing capacitors 32 and 34each to be charged to a value V/2 and a voltage V is present across theoutput terminals 36 and 38. The negative half cycle of the signal on leg30B causes current to flow through diode 40 and capacitor 34 becomesfurther charged. Capacitor 42 gets charged in the opposite direction andcapacitor 32 remains charged due to diode 44.

If only the signal on leg 30A were present, the output voltage acrossterminals 36 and 38 would be 2V, however, during the occurrence at thenegative half cycle of the signal on leg 30A, a positive half cyclebegins on leg 308 which is 120 degrees of phase with the signal on leg30A. The operation of the signal on leg 30B is the same as described forleg 30A except that diodes 52, 54 and 48 and capacitor 50 and involved.A sinusoidal signal on leg 30C occurs l degrees after the signail on leg30B and operates in a similar manner to the signals on legs 30A and 308except that diodes 60, 62 and 56 and capacitor 58 are employed. Thethree symmetrical circuits forming the three phase rectifier areconnected in parallel across the output terminals 36 and 38 with theresult that the signals from each circuit add together and the resultantoutput signal across terminals 36 and 38 is 3V where V is the amplitudeof the three phase signal from winding 30.

A distinct advantage of the circuit of FIG. 2 is the reduced ripplevoltage. Ripple is an inverse function of the frequency, resistance andcapacitance (mRC) of the rectifier circuit. Thus, the larger theresistance, capacitance and frequency the smaller the resultant ripple.Most rectifier circuits operate at 60 cycles. Therefore, the frequencyis fixed and for power applications, a small resistance is desired inorder that a large current can be produced. Thus, to reduce ripple in asingle phase rectifier as shown in FIG. 1, a prohibitively largecapacitance must be provided. In the circuit of FIG. 2, however, each ofthe symmetrical circuits contributes a signal three times morefrequently into the parallel output capacitors 32 and 34, that is, threetimes more signal is provided for every half cycle of each phase in thethree-phase circuit of FIG. 2. This means that the effective frequencyis three times that of the single phase circuit and the parallelconnection produces three times the capacitance. More particularly, inFIG. 2, the two capacitors 32 and 34 provide the equivalent of three ofthe capacitors l2 and three of the capacitors 14 of the circuit shown inFIG. 1. Thus, the two capacitors in FIG. 2 function more effectivelythan if the three pairs of capacitors of FIG. 1 were connected inparallel. Since the frequency (w) is three times greater and thecapacitance (C) is three times greater, (wRC) is nine times larger thanin the single phase circuit and thus, the ripple parameter is greater bya factor of nine rather than three, reducing the ripple appreciably.

What has been described in a three-phase voltage tripling rectifiercircuit including a unique combination of capacitors and diodes whichform three symmetrical circuits. An advantage of the three-phaserectifier circuit is that it operates with a substantially low ripplevoltage.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formand details may be made therein without departing from the spirit andscope of the invention] What is claimed is:

l. A three-phase voltage tripling rectifier circuit comprising:

a three-phase winding including three legs for producing a three-phaseAC voltage;

three identical circuits composed of diodes and capacitors including twooutput capacitors, each one of said circuits connected to a separate oneof said legs of said winding;

and a pair of series connected output capacitors connected to said threeidentical circuits for producing a rectified output voltage three timesthe amplitude of said three-phase AC voltage wherein said threeidentical circuits whose outputs are connected in parallel and saidseries connected output capacitors are equivalent to capacitors of saidthree identical circuits connected in parallel.

2. A three-phase voltage tripling rectifier circuit according to claim 1wherein each of said three identical circuits includes a back biaseddiode between the associated one of said legs of said winding and oneside of said pair of series connected output capacitors;

a pair of series connected diodes connected to the other side of saidpair of series connected output capacitors; and a capacitor connectedbetween said back biased diode and the junction between said pair ofsaid series connected diodes.

3. A three-phase voltage tripling rectifier according to claim 2 whereinsaid legs of said three-phase winding are connected to a wye arrangementat a common junction and wherein said common junction of said threephasewinding is connected to each of said pair of series connected diodes ofsaid identical circuits and to the junction of said pair of seriesconnected output capaci-

1. A three-phase voltage tripling rectifier circuit comprising: athree-phase winding including three legs for producing a three-phase ACvoltage; three identical circuits composed of diodes and capacitorsincluding two output capacitors, each one of said circuits connected toa separate one of said legs of said winding; and a pair of seriesconnected output capacitors connected to said three identical circuitsfor producing a rectified output voltage three times the amplitude ofsaid three-phase AC voltage wherein said three identical circuits whoseoutputs are connected in parallel and said series connected outputcapacitors are equivalent to capacitors of said three identical circuitsconnected in parallel.
 2. A three-phase voltage tripling rectifiercircuit according to claim 1 wherein each of said three identicalcircuits includes a back biased diode between the associated one of saidlegs of said winding and one side of said pair of series connectedoutput capacitors; a pair of series connected diodes connected to theother side of said pair of series connected output capacitors; and acapacitor connected between said back biased diode and the junctionbetween said pair of said series connected diodes.
 3. A three-phasevoltage tripling rectifier according to claim 2 wherein said legs ofsaid three-phase winding are connected to a wye arrangement at a commonjunction and wherein said common junction of said three-phase winding isconnected to each of said pair of series connected diodes of saididentical circuits and to the junction of said pair of series connectedoutput capacitors.